Behind its overall defense and 13 points and four blocks from Benilson Lumani, sixth-seeded Portland pulled off an upset Saturday in the Class A South boys basketball tournament, beating No. 3 South Portland, 34-33, in a quarterfinal at the Portland Expo.

The teams split two games during the regular season. Portland (14-6) advances to a semifinal at 6 p.m. Thursday against No. 2 Sanford.

South Portland (15-4), ranked No. 5 in the state in the latest Varsity Maine poll, was held to six points in the first half. The Red Riots had 13 turnovers, and Portland’s Loic Ramazani (10 points, nine rebounds, four steals) and Cordell Jones combined to limit first-team SMAA all-stars Gabe Jackson and Darius Johnson to two points and just two shot attempts. Jackson finished with six points, Johnson with five. Portland’s first-team all-conference pick, Lucas LeGage, did not score.

The Bulldogs’ 16-6 lead at halftime could have been larger if not for their own poor shooting (6 of 25).

South Portland got back into the game with a pair of Leonel Despacho 3-pointers in the fourth quarter. The Red Riots twice had a chance to tie the game at the free-throw line, but Despacho missed 2 of 3 attempts after he was fouled attempting a 3-pointer, and then Johnson made only 1 of 2, leaving the Bulldogs with a 31-30 advantage.

Portland got a layup from Maddox Meas and one free throw from Ramazani to lead by four points with about 12 seconds to play. Despacho (team-high 10 points) hit a 3-pointer at the buzzer.